cis-acting translational effects of the 5' noncoding region of c-myc mRNA.

Abstract

We have previously shown that the 5' noncoding region of mouse c-myc mRNA has a negative effect on translational efficiency in a rabbit reticulocyte lysate (A. Darveau, J. Pelletier, and N. Sonenberg, Proc. Natl. Acad. Sci. USA 82:2315-2319, 1985. We wanted to localize and characterize the inhibitory translational element(s) in the mRNA and to study its effect in other in vitro and in vivo systems. Here we report that the restrictive element is confined to a 240-nucleotide sequence of the 5' noncoding region of mouse c-myc mRNA and that this sequence acts in cis to inhibit the translation of a heterologous mRNA. In addition, we report that the cis-inhibitory effect is also exhibited in microinjected Xenopus oocytes and wheat-germ extracts but not in HeLa cell extracts. Transfection of corresponding plasmid DNA constructs into several established cell lines did not produce the cis-inhibitory effect. A model to explain these results is presented.

Differential expression of Myc1 and Myc2 isoforms in cells transformed by eIF4E: evidence for internal ribosome repositioning in the human c-myc 5′UTR

“…The 5'UTR of human c-myc mRNA is inhibitory for translation in most systems, including Xenopus oocytes, but not in COS cells or HeLa extracts (Parkin et al, 1988;Fraser et al, 1996). De®nitive conclusions from these studies were hampered by the short half-life of Myc and its autoregulatory suppression when overexpressed (Pause and Sonenberg, 1993;De Benedetti et al, 1994).…”

eIF4E – from translation to transformation

“…Deletion mutations in the c-myc 5'UTR, which are present in several Burkitt lymphomas (resulting from translocation of the c-myc gene), result in enhanced translation of the c-Myc mRNA (Saito et al, 1983;Darveau et al, 1985;Parkin et al, 1988;Carter et al, 1999;Willis, 1999). cmyc is implicated in several biological processes such as cell growth, proliferation and apoptosis (reviewed in Gartel and Shchors, 2003;Hermeking, 2003;Levens, 2003;Pelengaris and Khan, 2003).…”

C-Myc 5′ untranslated region contains an internal ribosome entry segment

“…Transcripts initiated at P0, P1 and P2 give rise to 5' untranslated regions of approximately 1000, 600 and 400 nucleotides respectively. In vitro studies on the 5' UTR of the P2 transcript have demonstrated that this region is highly structured and inhibitory to ribosome scanning (Darveau et al, 1985;Parkin et al, 1988). To determine the eect of 5' UTR in vivo, we inserted a 396 bp segment into the plasmid pGL3 (Promega) directly upstream of the coding region for ®re¯y luciferase to create the plasmid construct pGL3utr ( Figure 1a).…”

“…However, early studies in vivo examining translational eciencies of c-myc mRNA in Burkitt's lymphoma cell lines suggested that both truncated and full length transcripts were translated with equal eciencies (Nilsen and Maroney, 1984). Moreover, when expressed in numerous cell lines or translated in HeLa cell extracts the 5' UTR does not inhibit translation of either c-myc or reporter genes (Butnick et al, 1985;Parkin et al, 1988). This disparity suggests that non-canonical factors, which are lacking in rabbit reticulolysate and wheat germ extract, facilitate c-myc translation through the 5' UTR in vivo (Parkin et al, 1988).…”

“…In addition, c-myc mRNAs lacking exon 1 were found to be translated more eciently in vitro when compared to full length transcripts (Darveau et al, 1985). Furthermore, a 240 nt restrictive element within exon 1 of murine c-myc was isolated and shown to inhibit translation of heterologous mRNAs in rabbit reticulocyte lysate and wheat germ extract (Parkin et al, 1988) demonstrating that the 5' UTR is highly structured and inhibitory to the scanning mechanism of translation. However, early studies in vivo examining translational eciencies of c-myc mRNA in Burkitt's lymphoma cell lines suggested that both truncated and full length transcripts were translated with equal eciencies (Nilsen and Maroney, 1984).…”